I ran HP manifolds on my engines for years. Performance isn't really a problem with HP manifolds, you can make enough power with them to run a lot faster than most cars are legal for. But I eventually got tired of cooking valve covers and valve cover gaskets so I switched to headers. Fitting headers into a BB A body with a manual trans isn't going to be easy. I would not go with full length headers for your car. Some shorty headers or maybe a tri-y will work. The Schumacher headers won't fit out of the box with a Z bar but they can be modified. I'm not sure if Schumacher is still in business. Last time I checked he was out of stock of everything. I redid a set of Schumacher headers for my car so they would work with my Z bar but it took some hours at a street rod fab shop so it wasn't cheap.
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